This invention relates to a photosensor array device and more particularly to an improvement of a line sensor utilized for direct contact type photosensor array devices such as a facsimile transmitter.
Recently, with a view to reducing the size and increase the operating speed and reliability of a facsimile transmitter, a photosensor array of the direct contact type has been proposed. Such a photosensor array device includes a line sensor in which a plurality of amorphous silicon film diodes having a photoelectric conversion performance are juxtaposed on a transparent glass substrate at a pitch of about 8/mm (about 125 microns), for example and the sensor is brought into direct contact with a manuscript to be transmitted for reading the manuscript with a magnification of 1(one). For transmitting a manuscript having a width of about 220 mm, it is necessary to provide about 1760 amorphous silicon film diodes, blocking diodes of the same number connected in series with respective film diodes for preventing crosstalk caused by the divergent flow of the photoelectrically converted signals, and a matrix wiring acting as lead wires for reading out the signals.
With the type photosensor array device of this construction, since it uses amorphous silicon for fabricating the photoelectric converting elements and since it is extremely difficult to lead out a great number of signal wires for read out bits, a matrix wiring construction as shown in FIG. 1 has been proposed. More particularly, reference numeral 1 designates a common electrode selector, 2 photoelectric converting elements made of amorphous silicon film diodes, for example, 3 blocking diodes for preventing cross-talk, 4 signal wirings acting as read out signal lines, and 5 an electrode selector.
When transmitting a manuscript of about 220 mm width with the sensor array device of this construction, in order to provide a matrix wiring consisting of about 1760 signal wirings 4, it is necessary to use a multilayer wiring structure.
To explain the multilayer wiring structure, one example of the line sensor of the direct contact type photosensor array device using diodes as crosstalk preventing elements will be described with reference to FIG. 2. As shown, the line sensor comprises a transparent glass substrate 21 to which a manuscript to be transmitted, not shown, is directly contacted, and a plurality of chromium electrodes 22 formed on the substrate. In this example, about 1760 sets of electrodes 22 are juxtaposed at a pitch of 125 microns in the direction of array. Each set comprises a common electrode 22a, a connector electrode 22b and an individual electrode 22c which are aligned and spaced from each other at predetermined spacings. The line sensor further comprises a photoelectric conversion photodiode 23 made of amorphous silicon deposited on one end of the connector electrode 22b, a crosstalk preventing blocking diode 24 made of amorphous silicon deposited on the other end of the connector electrode 22b, a passivation film 25 made of Si0.sub.2 or other insulator and adapted to protect opposite end portions 23a and 23b of the photodiode 23 as well as opposite end portions 24a and 24b of the blocking diode 24, a transparent film electrode 26 deposited on the passivation film 25 for electrically interconnecting the photodiode 23 and the common electrode 22a, an upper electrode 27 formed by vapor depositing aluminum on the passivation film 25 and adapted to electrically interconnect the blocking diode 24 and the individual electrode 22c, a matrix wiring insulation film 10 formed on the individual electrode 22c, a matrix wiring 28 formed by vapor depositing aluminum on the insulation film 10, and connector 29 for the matrix wiring formation.
Each photodiode 23 and blocking diode 24 has an n-type lower layer, an i-type intermediate layer and a p-type apper layer. The matrix wiring 28 and connector 29 are also covered with the passivation film 25.
With this line sensor, since the photodiode 23 which detects light reflected by the manuscript for converting the light into an electric signal, and the blocking diode 24 acting to prevent crosstalk of the matrix wiring 28 are formed separately, it has been necessary to form the upper electrode 27 by vapor depositing aluminum after protecting the end portions 23a, 23b, 24a and 24b of the diodes 23 and 24 with the passivation film 25 made of Si0.sub.2 so as to prevent short circuiting between the ends, especially, opposite ends 23b and 24a. To form the upper electrode 27 on the passivation film 25, a through-hole 25a must be formed which passes through the passivation film 25. To this end, highly precise selective etching of the passivation film 25 and the blocking diode 24 is required, which decreases the yield rate of the line sensors.